1. Field of the Invention
The present invention generally relates to an RFID cargo/storage container tamper seal, and, more particularly, to a passive UHF omnidirectional power-free cargo/storage container tamper seal suitable for sea-going cargo containers comprised of a three-dimensional helix-shaped antenna.
2. Description of the Related Art
Container tamper seals commonly used in the current transportion or storage industry include mechanical tamper seals and active RFID tamper seals. By way of comparison, conventional mechanical tamper seals have the advantage of low-cost but are also known to have drawbacks in terms of scanning and management due to their inability to be read in a fully automatic way during customs clearance. Conversely, active RFID tamper seals are more costly but are capable of providing automation of container transportation; however, such tamper seals cannot realize long-distance transmission and also typically have a directional issue to overcome.
RFID tamper seals have been tested and employed in various ports under the American Customs-Trade Partnership Against Terrorism (C-TPAT) initiative, and have been proven to be able to improve on and upgrade the automation of customs clearance over existing mechanical tamper seals. Moreover, RFID technology has become increasingly popular because it enables automation of container transportation, replacing manual operation to thus increase efficiency.
In practical application, an RFID tamper seal (Smart-Seal) is disposed at a place where the container is opened, that is, usually on the doorbolt lock latch. Typically, two tamper seals are disposed on a container assembly consisting of two 20-foot containers, one on the front-facing container and one on the rear-facing container, or a single tamper seal is provided at the rear of a full-sized 40-foot container. At a scanning distance of 3.5 meters, real-time identification can be achieved when the container vehicle is stopped or moving under the speed of 30 km/hr while passing through an RFID reader provided at Customs. In the prior art, U.S. Pat. No. 2007/0194025A1 discloses the foregoing smart-seal as shown in FIG. 1, in which an electronic tamper seal 60 comprises an insertion bolt 40 and a main body 30, the insertion bolt 40 comprising an antenna 45 and the main body 30 having an RFID chip 35, the main body 30 being coupled to the insertion bolt 40 on the door bolt latch 52. Upon customs clearance, the RFID reader 50 at Customs senses the electronic tamper seal 60 and automatically provides the electronic tamper seal 60 with an energetic electromagnetic wave 50a to enable the RFID chip 35 equipped therein to transmit an identification electromagnetic wave 60a comprising an ID code back to the RFID reader 50.
FIG. 2 is a perspective exploded diagram illustrating the foregoing RFID tamper seal, in which the tamper seal 60 comprises a main body 30 having a cavity and an insertion bolt 40 in a cylindrical shape. The main body 30 comprises a pair of conductive pins 35a, an identification chip 35 electrically connected to the conductive pins 35a, a pair of connecting pins 33 electrically connected to the conductive pins 35a, and a C-shaped ring 34 configured in the cavity of the main body 30. The insertion bolt 40 comprises a pair of antenna legs 45a electrically connected to an antenna 45 disposed on the top of the insertion bolt 40. The insertion bolt 40 further comprises a ring-shaped groove A adapted to combine with the C-shaped ring 34 when the insertion bolt 40 is received in the main body 30, and further allow the connecting pins 33 disposed on the conductive pins 35a of the main body 30 to be electrically connected to the antenna legs 45a disposed on the insertion bolt 40, thereby allowing identification signals from the RFID chip 35 to be transmitted therefrom via the conductive pins 35a and antenna legs 45a. 
From the above disclosure and figures, it is noted that the electromagnetic wave transmitted by the antenna 45 has a directional limitation (as shown in FIG. 1) due to the planar configuration of the antenna 45 of the electronic tamper seal 60. Further, the radiated field pattern thereof, as shown in FIG. 3., is uneven in zones A, B and C due to configuration limitations of the antenna legs 45a, the conductive pins 35a, and the identification chip 35. As a consequence, it is necessary to install and fasten the RFID tamper seal 60 on the door bolt latch with the orientation depicted in FIG. 1 with the antenna directed at the reader to allow the RFID reader 50 to better sense the antenna 45 so that the reader 50 can receive the electromagnetic waves 60a conveying the identification signal transmitted from the RFID tamper seal 60 for access and customs clearance. Further, as shown in FIG. 2, application of the tamper seal also requires precise alignment in order for the electronic tamper seal to function properly when the antenna legs 45a disposed on the insertion bolt 40 are engaged with the conductive pins 35a of the main body 30.
In summary, while the foregoing RFID tamper seal improves on and has advantages over mechanical tamper seals of the prior art, such as convenience in usage and quick detection of any tampering, it also has the aforementioned structural and usage limitations involving inconvenience in application and usage, particularly with respect to the directional issue.